With the seat up at a real pedalling position it moves back and away from the on-paper measurement. Many also include stack and reach measurements, but fork rake, bottom bracket drop and trail are not as common. How far the bottom bracket is below a line drawn between front and rear axles. Where the top tube is horizontal the Effective Top Tube and Actual Top Tube will be identical. here's a trig calculator - side C will be your seat tube length and angle B your seat angle, side A will give the resultant setback of the frame. Aero seat posts and plenty of other sizes available means there's no such thing as a 'standard' seatpost diameter. What is the ideal fit? The current version of BikeCAD is 16.0. Length originally specified as part of the complete bike. When standing, reach and stack define your position over the bike, as your only contact points are your hands and your feet. Chainstay length is one of the two components that make up your wheelbase and, again, contributes significantly to your frame’s handling characteristics.
And this is where we started to generate more than one seat angle and some confusion.
The virtual points to the center of the bottom bracket. Your frame’s wheelbase is the distance between the front and rear axles. Best road bike: find the right bike for your budget, Best mountain bike: everything you need to know, Get funky and light with two limited-edition products from SunRinglé and Hayes, Cheap gravel bikes: affordable adventure bikes for dirt, gravel and commuting, Best cycling apps | 18 of the best iPhone and Android apps to download, This one super-cheap hack will stop cold feet when cycling this winter, Get you and your bike ready for winter with discounted cold weather kit, Reach and stack – and why they’re important numbers, A clinometer to measure angles (there are free smartphone apps you can download), A long spirit level (or you can use the clinometer app and a straight piece of wood), A plumb line (or you can improvise with string and a couple of blobs of Blue Tack).
Looking to road bikes, performance race bikes will typically have a longer reach than endurance bikes to stretch a rider out, creating a lower frontal profile to improve aerodynamics. Stem length is directly linked to the steering arc of the handlebars and so has a huge effect on a bike's handling. Older bikes frequently had horizontal top tubes, but now sloping tubes are much more common. (Conversely, shorter chainstays can make a bike feel more playful - quicker to turn and easier to manual - at the expense of wheelbase length.) The head tube angle refers to the angle of the head tube to the ground and will commonly be described as either 'slack' or 'steep'. That’s not true of mountain bikes, where the frame size is usually marked S, M, L etc. The parameters affecting road bike handling have settled on a formula that’s known to work for each category and differs little between brands. As mentioned, increasing the length of the bike's stem can increase the rider reach, stretching them out and creating a lower frontal profile. A steep head tube angle is found on performance road race, requiring less effort to steer which is better for high-speed handling.
For a related dimension, see Effective top tube length.
Treat with caution! Now that you know everything there is to know about geometry charts, check out other BikeExchange guides to provide all the info you need to know on a variety of topics; The Ultimate Guide to Buying a Mountain Bike, Aero vs Endurance vs Lightweight Road Bikes Explained, Follow BikeExchange: Email | Facebook | Twitter | Instagram | YouTube | STRAVA. Now many bikes’ top tubes will have a slope. Regardless of the frame reach, a rider's reach can be manipulated by changing the saddle set-back position and stem length. On a suspension fork this is measured with fork uncompressed.
A modern enduro bike might be designed around a 40mm stem, an XC bike (or any MTB a few years old) might assume a 70mm stem. The below image shows an example of how a steeper headtube angle reduces the amount of trail and as a consequence will speed up the bike's handling. He was into gravel before it was even invented, riding a cyclocross bike across the South Downs and along muddy paths through the Chilterns. If you’re using Blue Tack, make sure that the blob at the end of the string is fairly symmetric and your string hangs down straight otherwise your measure may be off. Useful because you can measure it and helps you work out how much seatpost you need.
The head tube length is measured from the bottom to the top of the head tube. It's important to know straight off the top that bikes are not the same in terms of geometry and size. A slacker (smaller) head angle gives more stable handling at speed but can feel wander-y while going slower.